In an optical waveguide device such as an optical modulation element and a second-order higher harmonic generation element, a pair of ridge grooves is formed in an optical waveguide substrate, and a ridge optical waveguide is formed between the ridge grooves. Then, the optical waveguide substrate is attached to an independent support substrate, and it is known that phase matching is attained by configuring the optical waveguide substrate to be a thin plate equal to or less than 10 μm in thickness.